1. Field of the Invention
The present invention relates to a digitizing apparatus with an extension-intersection measuring function for obtaining form data of a three-dimensional model by scanning the surface of the three-dimensional model using a stylus of a tracer head.
2Description of the Prior Art
When the coordinates of a point which does not exist on a three-dimensional model, that is, the coordinates (X.sub.c, Y.sub.c, Z.sub.c) of, for example, a point P.sub.c at y=Y.sub.c on intersection line L.sub.c of planes A and B of a three-dimensional model M shown in FIG. 1 is obtained a conventional digitizing apparatus, the X-coordinate and the Z-coordinate of two optional points P.sub.A1 and P.sub.A2 on the plane A at y=y.sub.c and the X-coordinate and the Z-coordinate of two optional points P.sub.B1 and P.sub.B2 on the plane B at y=y.sub.c are measured by utilizing a point measuring function. Then, an operator, with a personal computer or the like, obtains straight line L.sub.A passing through the points P.sub.A1 and P.sub.A2 and straight line L.sub.B passing through the points P.sub.B1 and P.sub.B2 in accordance with the coordinates of each of the points P.sub.A1, P.sub.A2, P.sub.B1 and P.sub.B2. The coordinates of the intersection (to be called "the extension intersection" hereinafter) becomes the desired coordinates (X.sub.c, Y.sub.c, Z.sub.c) of the point P.sub.c.
However, a problem arises in the above-described method for obtaining the coordinates of the extension intersection using the conventional digitizing apparatus in that a tremendous amount labor is required since an operator must effect measurements using the point measuring function or perform calculations using a personal computer or the like.